What is the difference between the front and back end?

Front

The "front end" of your website is what users see when they visit your site. It has a specific login for users that help provide and edit content but do not require access to the site's administrative controls. The front-end interface is used to make quick changes to existing Web pages ( articles). It is very similar is similar to other word-processing applications such as email editor or Microsoft Word. Once you log in, you will see an edit button for each article. Just click on the icon that looks like this to open the Joomla JCE Editor.

Back

The "back end" is the control panel that site managers, administrators and super administrators use to build and manage the the structure/content of a website. It includes all the tools available from the front but provides access to more advanced options such as menu edits, adding users and controlling the way content is displayed on a website.